CAIRO – A suspected Israeli airstrike against a weapons factory in Khartoum last week points to a possible escalation in a hidden front of the rivalry between Israel and Iran: The arms pipeline through Sudan to Islamic militants on Israel's borders.

Mystery still surrounds the blast, which killed four people. But analysts say the incident could indicate Iran is trying to send more advanced weapons via Sudan to Hamas in the Gaza Strip or Hezbollah in Lebanon — and that Israel has become more determined to stop it at a time of increased tensions over Iran's nuclear program.

Consensus has built among Israeli and Arab military analysts that the explosion just after midnight last Wednesday at the Yarmouk factory was indeed an Israeli airstrike as Sudan has claimed. Israel says it neither confirms nor denies being behind it. Sudan, in turn, denied on Monday that Iran had any connection to the factory's production.

In a show of support for the two countries' alliance, two Iranian warships — a helicopter carrier and destroyer that had been conducting anti-piracy patrols off East Africa's coast — docked this week at Sudan's main Red Sea port. The Iranian commanders were holding talks with Sudanese officers as part of the countries' "exchange of amicable relations," Sudan's military spokesman said.

Sudan's Foreign Ministry dismissed allegations of an Iranian connection to the Yarmouk facility, saying "Iran does not need to manufacture weapons in Sudan, be it for itself or for its allies."

Experts say that Sudan's value to Iran is not in its modest weapons production capabilities, but in its vast desert expanses that provide cover for weapons convoys bound for Gaza through Egypt's lawless Sinai Peninsula. Israel has long contended that Iran uses the route to supply Hamas. It appears to have struck the supply line at least once before, when a convoy in a remote part of Sudan was blasted by explosions in 2009 — though Israel never admitted to the attack.

The question now is: What would prompt Israel to conduct a bolder strike hitting a Sudanese government facility in the heart of the capital Khartoum?

The target may have been 40 shipping containers that satellite images show were stacked in the factory compound days before the explosion. Post-explosion imagery released Saturday by the Satellite Sentinel Project, a U.S. monitoring group, show six 52-foot-wide craters all centered at the spot where the containers had been, the blast's epicenter.

The group said the craters were consistent with an airstrike and that whatever it hit was a "highly volatile cargo," causing a powerful explosion that destroyed at least two structures in the compound and sent ordnance flying into nearby neighborhoods.

What was in the containers remains unknown — leaving observers to speculate.

Retired Israeli Brigadier General Shlomo Brom, a military expert, said there is a "strong possibility" that Israel had identified an "imminent threat" within the factory.

Brom, a research associate at the Institute for National Security Studies at Tel Aviv University, said the containers could have been part of Iran's efforts to smuggle "a new category of weapons" to Gaza. The weapons could be "something with air defense capability ... or could very well belong to the category of rockets and missiles, but just larger, stronger, and longer range," he said.

Gen. Sameh Seif Elyazal, a former Egyptian army general, said his understanding was that a strike was carried out against short-range missiles being assembled in the factory "under Iranian supervision," bound for the Hamas and Hezbollah militant groups. He said that his analysis was based on "private conversations with Israeli officials" that had been conveyed to him through others. He did not elaborate.

"Iran wants to put Israel under pressure from the north, through Hezbollah and from the east through Gaza," he said.

Iran has long backed Hamas, which took control of the Gaza Strip in 2007. Iran's relations with Hamas have been strained after the Palestinian militant group this year cut its ties with Syria — Tehran's biggest Arab ally — over that country's bloody civil war. Iran has since cut back some aid to the group, but a senior Hamas leader visited Tehran last month and Hamas officials say the group's military wing in particular continues to receive funding from Iran.

Iran "has sought alternate routes" for its arms shipments to Hamas after Israel cracked down on maritime lanes direct to Gaza that Tehran previously used, said Michael Eisenstadt, Director of the Military and Security Studies Program at the Washington Institute for Near East Policy.

The Sudan route "complicates matters for Israel," he said.

Hezbollah is another possible destination. But despite the civil war, Syria is believed to remain the primary route for Tehran to supply its powerful Shiite guerrilla ally in Lebanon.

Iranian arms shipments gain added significance amid the dispute of Iran's nuclear program, which Israel and the U.S. contend is aimed at producing a bomb. Israel has held out the possibility of attacking Iranian nuclear facilities. Iran denies any intention to build a bomb and has warned it will retaliate for any Israeli attack — raising fears Hezbollah, Hamas or other Iranian-backed militant groups would carry out strikes on Israel.

Speaking to Israel Radio after the Wednesday explosion in Khartoum, Israeli Vice Premier Moshe Yaalon said "there's no doubt that there is an axis of weapons from Iran via Sudan that reaches us, and not just us."

The contentions surrounding last week's explosion also point to the close ties between Iran and Sudan, dating back to the 1989 coup that brought President Omar al-Bashir to power, when Iran's Revolutionary Guard helped supply him weapons.

Though wanted by the International Criminal Court for alleged atrocities in the western Sudanese region of Darfur, al-Bashir visited Tehran most recently in August for a Nonaligned Movement summit. Iran has made significant investments in water and engineering projects in Sudan.

China is the main arms source for Sudan's government. But Iran, which signed a military relations deal with Khartoum in 2008, is also a supplier.

Notably, Khartoum appears to receive Iranian drones to use in its multiple domestic wars against rebel groups, said Jonah Leff, who monitors Sudan for the Small Arms Survey. Rebels shot down two such drones, in 2008 and in March this year.

An Iranian role at the Yarmouk facility remains uncertain. The facility, which opened in 1996, was touted by Sudan as a source of pride, showing its weapons manufacturing capabilities. Still, the factory only produces ammunition. Leff said there is no evidence Iranian weapons are being assembled there, suggesting it was beyond the facility's capabilities.

But, he said, workers from Yarmouk have traveled to Iran for training.

There have also been reports of Iranian experts residing at Yarmouk, said Hani Raslan, an expert on Sudan at the Ahram Centre for Political and Strategic Studies in Cairo. Raslan also said he suspects the strike was aimed at weakening the Iranian arms smuggling network.

Fawaz A. Gerges, who heads the Middle East Center at the London School of Economics, says the strike has its symbolic aspect as well, allowing Israel to "flex its muscle and capacity and will to strike."

"Regardless of what particular weapons were destroyed, Israel sent a message to Sudan and to Iran," Gerges said.